FIG. 1 illustrates a 3T-2S image sensor circuit obtained by combining two first-type image sensor circuits each including three transistors.
Referring to FIG. 1, a 3T-2S image sensor circuit 100 is obtained by combining two image sensor unit cells 110 and 120 each including three transistors. The 3T-2S image sensor includes two photodiodes PD0 and PD1 and four transistors M101 to M104. In the 3T-2S image sensor circuit 100, reset transistors M2 and M5 and conversion transistors M3 and M6 are shared by the two image sensor circuits 110 and 120 each including three transistors. The 3T-2S image sensor circuit 100 uses two transistors M103 and M104 commonly used for reset and conversion operations and two transmission transistors M101 and M102 respectively connected to the two photodiodes PD0 and PD1.
Here, since a reset signal Rx01 applied to a gate of the reset transistor M103 is enabled when one of two charge transmission control signals Tx0 and Tx1 respectively applied to gates of the transmission transistors M101 and M102 is enabled, the reset signal Rx01 is denoted by using ‘01 (zero and one)’. A selection signal Sx is enabled in response to the two charge transmission control signals Tx0 and Tx1, respectively.
FIG. 2 illustrates a 3T-2S image sensor circuit obtained by combining two second-type image sensor circuits each including three transistors.
Referring to FIG. 2, a 3T-2S image sensor circuit 200 is obtained by combining two image sensor unit cells 210 and 220 each including three transistors. The 3T-2S image sensor includes two photodiodes PD0 and PD1 and four transistors M201 to M204. Reset transistors M12 and M15 and conversion transistors M13 and M16 are shared by two image sensor circuits 210 and 220 each including three transistors. The 3T-2S image sensor circuit 200 senses and transmits electric charges corresponding to image signals generated by the two photodiodes PD0 and PD1 by using two shared transistors M203 and M204 and the two transmission transistors M201 and M202.
In FIG. 1, a terminal of the reset transistor M103 and a terminal of the conversion transistor M104 are connected to a selection signal Sx. Unlike FIG. 1, in FIG. 2, a terminal of the reset transistor M203 is connected to the selection signal Sx, and a terminal of the conversion transistor M204 is connected to a voltage source Vdd.
As described, a single 3T-2S image sensor circuit obtained by combining two image sensor circuits each including three transistors may be laid out in various manners. However, a case where four image sensor circuits combined in a single unit cell has not been particularly published.